Identification of Postharvest Pathogens of Amorphophallus muelleri and Indoor Screening of Fungicides

Konjac （Amorphophallus muelleri）, a genus of tuberous plants in the Araceae family, is one of high-value crops in Southwest China. This study aimed at identifying the main pathogens causing tuber rot during storage ofA. muelleri and screening the effective fungicides, so as to prolong the storage period ofA. muelleri and decrease the losses. Isolation and identification, as well as pathogenicity test and retro-inoculation experiments were made for the pathogen causing tuber rot during storage ofA. muelleri in Kunming city, Yunnan province, China. The effective fungicides for the main pathogens were also screened in the laboratory. Six fungi were identified as the pathogens causing tuber rot of A. muelleri, which were Fusarium solani （Mart,） Sacc., Fusarium oxysporum Schlecht., Botrytis cinerea Pers., Alternaria alternata （Fr.） Keissl., Rhizopus nigricans Ehrenb., Penicillium ulaiense Hsieh, Su ＆ Tzean. The main pathogens causing postharvest diseases ofA. muelleri were F. solani, F. oxysporum and B. cinerea. The isolation frequencies of them were 33.9%, 10.5% and 19.4%, respectively. After artificial inoculation, the incidence of tubers infected by F. solani, F. oxysporum and B. cinerea was 100%, 83% and 95%, respectively. The results of chemical screening showed that, in potato dextrose agar （PDA） media plate, the compounds Fludioxonil （50% WP） and Boscalid （50% WG） were the most effective in controlling the three main pathogens, and the average effect reached more than 97%. The test of fungicidal antisepsis on tubers consisted ofA. muelleri being dipped in the 9,000x diluted solution of Fludioxonil （50% WP） or in the 3,500x diluted solution of Boscalid （50% WG） for 3 min and stored at room temperature （25 ℃） for 7 d and 15 d, respectively. The fungicidal effects of Fludioxonil against F. solani, F. oxysporum and B. cinerea for 7 d and 15 d were 88.6%/83.2%, 90.1%/84.7% and 93.0%/91.5%, respectively, whereas the fungicidal effects of Boscalid were 87.0%/85.3%, 89.0%/85.6% and 89.2%/89.1%, respectively. The results may provide useful information for the control ofpostharvest diseases ofA. muelleri.

Toxicity of 26 Fungicides against and Synergistic Effects of Binary Mixtures on Oidium heveae

[Objective] This study was conducted to determine the toxicity of 26 fungicides against Oidium heveae and the synergistic effects of their binary mixtures.[Method] The sensitivity of O.heveae to 26 fungicides was determined in vitro and in vivo by calculating EC50 values.Horsfall＇s toxicity rate was preliminarily employed to predict the type of joint action of 180 two-way mixtures,based on which the interaction level of the potentially synergistic mixtures was validated by Sun and Johnson＇s co-toxicity coefficient.[Result] Triflumizole,pyraoxystrobin,flufenoxystrobin,epoxiconazole,pyrametostrobin,flusilazole,pyraclostrobin and tetraconazole were the most potent inhibitors of both spore germination and mycelial growth.An ‘in vitro-in vivo＇ integrated strategy is proposed for screening the inhibitors of O.heveae,according to the fact that data obtained in germination experiment are able to reflect to some extent the effectiveness of fungicide confirmed by pot experiment.Results achieved by Horsfall＇s were in line with that validated by Sun and Johnson＇s,the Horsfall＇s seems to be a convenient means to assess rapidly the potential interaction type and level of fungicides in a binary mixture.Nineteen mixtures interact synergistically：epoxiconazole ＋ pyraclostrobin at the mixing ratio of 6：4,8：2;tetraconazole ＋ flufenoxystrobin at 1：9,2：8,3：7 and 4：6;triadimefon ＋ flufenoxystrobin at 9：1;triflumizole ＋ flufenoxystrobin at 8：2;flusilazole ＋pyrametostrobin at 7：3,8：2 and 9：1;tetraconazole ＋ pyrametostrobin at 6：4;triadimefon ＋ pyrametostrobin at 5：5,8：2;triflumizole ＋ pyrametostrobin at 7：3,8：2;tetraconazole ＋ pyraoxystrobin at 9：1;triflumizole ＋ pyraoxystrobin at 8：2,9：1.[Conclusion] The single fungicides and their binary mixtures are expected to serve as the alternatives to triadimefon and the alternate use of them could delay the buildup of resistant O.heveae isolate.